Rebuild, What do I do???

[atf8611]

I have the top end appart, and now i am wondering what parts i have to replace to rebuild it. What do I do with the head? Do I have someone do somthing with the valves? what do i do with the cylinder? Do i need somthing done with that? I will be replacing the piston, where should i get a new one? Thanks for any help.

The reason for the rebuild was becuase i lost compression. after tearing it apart, i cant find anything obviously wrong with it, so i will just replace the usual and that should take care of it? The cylinder looks like its still in real good shape, it still has cross hatch marks.

Edit: bike is a 99 wr400

[Pincushion]

Have a repupatble shop inpspect the head & replace the stem seals. Since the valves are stainless chances are it'll require nothing more than a cleaning and seals replaced. Hone the cylinder and install a new piston/rings. I used a Wiseco 12.5:1 and have had no issues, but some complain they slap around in the bore. You can buy the Wiseco kit from most any mail order place or get OEM through the dealer of TT store.

[atf8611]

Have a repupatble shop inpspect the head & replace the stem seals. Since the valves are stainless chances are it'll require nothing more than a cleaning and seals replaced. Hone the cylinder and install a new piston/rings. I used a Wiseco 12.5:1 and have had no issues, but some complain they slap around in the bore. You can buy the Wiseco kit from most any mail order place or get OEM through the dealer of TT store.

Do i have to have someone hone the cylinder? if i do that, do i need a larger piston? what else would be done with the valves. i think that they are the cause of my compression loss.

[1rkcooper]

To check the valves for leaks pour some fluid into the intake port and hold it in such a way that if your seating is bad the fluid will leak through the valve, then do the same for the exhaust side. Not a perfect test but should give you an idea if the valve are seating ok.

[bluebike1999]

go here to identify your part numbers

http://www.yamaha-motor.com/star/myyamaha/prompt/L3N0YXIvcGFydHMvaG9tZS5hc3B4/Parts%20Catalog/starthere.aspx

then go here to get genuine yamaha parts direct from japan.

no middle man, no yamaha stealer/dealer

http://www.jp-parts.com/index.html

even if you dont get them here, get a quote from Maki to show whoever you get your bits from how much they should be and see what you can do.

I have been told to avoid wiseco pistons on wr/yz but now i have said that, every person with a wiseco piston will tell you they are good. just watch.

good luck

[atf8611]

To check the valves for leaks pour some fluid into the intake port and hold it in such a way that if your seating is bad the fluid will leak through the valve, then do the same for the exhaust side. Not a perfect test but should give you an idea if the valve are seating ok.

already did that, and it looks like a few are leaking. now i just need to find someone to do the work. thanks for the help guys. any more input on what kind of piston?

[Tsk350]

go here to identify your part numbers

http://www.yamaha-motor.com/star/myyamaha/prompt/L3N0YXIvcGFydHMvaG9tZS5hc3B4/Parts%20Catalog/starthere.aspx

then go here to get genuine yamaha parts direct from japan.

no middle man, no yamaha stealer/dealer

http://www.jp-parts.com/index.html

even if you dont get them here, get a quote from Maki to show whoever you get your bits from how much they should be and see what you can do.

I have been told to avoid wiseco pistons on wr/yz but now i have said that, every person with a wiseco piston will tell you they are good. just watch.

good luck

Does this web site work with shipping to U.S.A.?

[Tsk350]

[/quote/]I have been told to avoid wiseco pistons on wr/yz but now i have said that, every person with a wiseco piston will tell you they are good. just watch.

good luck[/quote/]

Wiesco is ok for a two stroke because they are lighter than a stock piston and you will be changing them out on a regular basis. I had them in my Banshee and if I ran alcohol I would burn the centers out so I went back to oem and never had a burnt piston. But as for a 4 stroke I would always go with OEM. There just a little tougher!!

[Numskull]

Have a reputable machine shop check your head over. If your seats are not cracked and your valves not bent, you can face the valves, and grind the seats, then "tip" the valves to the middle of the shim range.

I would probably bore the cylinder one size over and install new piston and rings while I had her tore down. Then do a search here on "break in" or "ring seal"

Dont forget to get a new timing chain.

[atf8611]

Have a reputable machine shop check your head over. If your seats are not cracked and your valves not bent, you can face the valves, and grind the seats, then "tip" the valves to the middle of the shim range.

I would probably bore the cylinder one size over and install new piston and rings while I had her tore down. Then do a search here on "break in" or "ring seal"

Dont forget to get a new timing chain.

how much does it cost to bore it one size over. i was told that it would have to be resleeved because of the nickasil(sp?) plating?

[bluebike1999]

Does this web site work with shipping to U.S.A.?

email and ask

[Numskull]

heres a link where Indy explains what nikasil is

It sounds like your head is the problem here, so you could probably get away with just fixing the head and putting it back together the way pincussion explained. I guess it depends on you and your budget. I think I read somewhere you can get a new cylinder for $250, new head for $500, a complete head for $700. This is just information Ive read while trolling the forums ?

I dont know what it would cost for a bore and plating. Maybe someone else can chime in and give you some links to a recommended machine shop.

[atf8611]

heres a link where Indy explains what nikasil is

It sounds like your head is the problem here, so you could probably get away with just fixing the head and putting it back together the way pincussion explained. I guess it depends on you and your budget. I think I read somewhere you can get a new cylinder for $250, new head for $500, a complete head for $700. This is just information Ive read while trolling the forums ?

I dont know what it would cost for a bore and plating. Maybe someone else can chime in and give you some links to a recommended machine shop.

I have the head at a shop being looked at now, and they said it would be in the area of $100 to get it fixed. on the reccomendation of the machine shop, i am just going to get a standard piston and leave the cylinder alone. i should have it all back together for around $300 total with piston, gaskets, and labor for the head. thanks for your help, i will keep you posted on how this goes.

[MotoGoalie]

I would probably bore the cylinder one size over and install new piston and rings while I had her tore down. Then do a search here on "break in" or "ring seal"

Dont forget to get a new timing chain.

WTH? He doesn't need to bore anything out if the Nikasil cylinder is in good shape. It just needs a quick hone to get the crosshatch revived.

[atf8611]

WTH? He doesn't need to bore anything out if the Nikasil cylinder is in good shape. It just needs a quick hone to get the crosshatch revived.

yeah its still in great shape. how do i hone it? thanks!

[426WROhio]

Your local shop can do a compression check to determine just how much leakage you are having on your top end. 5 to 8% range is said to be okay. (I had 60...) If you do not have the auto decompression, I recommend it! My cam tensioner went "bad", cam chain jumped 2 teeth. REPLACE your cam chain if you have install the decomp exhaust camshaft. I also had to have my valves seat cut, but they also repalced the springs, etc. The "unit price" for recut valves was $150, but they are like new.

Hot Cams Exhaust Auto decompression - $ 189.95 - ATR565054

(Note: due to chain and sprocket size differences the shop would not install the 03 YZ 450 exhaust cam)

Cam Chain - $34.95

They did hone cylinder and replaced it, I believe, with stock piston - YA5NG-11631-10-00 ($146.05)

My bike is a 01 WR 426, so part #'s will be different on Yamaha parts, but I beleive the hot cams part # stays the same.

I envy those that have the time, tools and ability to do this work, but I can't/don't. I respect that you can! ? All of my work done was 9.9 hours @ $55 an hours, I had to fork over $545 to get mine back on the trail! But in the end, I'd do it again if I had to!!!! ?

I hope this is of some help! (when I posted this, I didn't see there was a second page of replies - my bad.)

[MotoGoalie]

yeah its still in great shape. how do i hone it? thanks!

do a search on honing cylinders by grayracer. He has good advice if you want to do it yourself. I think a machine shop or bike shop can do it real quick for some small fee.

Do the search as you need to wash it out thoroughly and some people have advice on dry builds versus wet builds. Here is what I found.

https://www.thumpertalk.com/forum/search.php?searchid=1293330

It will be worth your time.